Commercial photovoltaic systems consist of large arrays of photovoltaic (PV) panels, which together conventionally generate between thirty kilowatts and one megawatt of power in full sunlight. Such systems are often grid-connected and located on flat-roofed commercial buildings for economic, safety and security reasons. Since the average photovoltaic panel used in these systems produces a maximum power of about one hundred fifty watts, there are conventionally between several hundred to several thousand individual photovoltaic panels in a commercial system.
The arrays of photovoltaic panels are conventionally connected electrically in multiple strings. Each string consists of ten to twenty or more photovoltaic panels wired in series, generating a maximum current of between five and ten amps at a maximum voltage of five hundred to six hundred volts (DC). A conventional one hundred fifty kilowatt commercial photovoltaic system has about one thousand photovoltaic panels in the array and may cover an area of approximately forty thousand square feet. The panels are arranged in fifty to one hundred strings, which are then subsequently connected in parallel in string combiners and wired to one or more inverters.
An inverter performs the function of converting the direct current power produced by the array of photovoltaic panels to alternating current for use by the customer, or for feeding back to the utility power grid. For such a system, the inverter weighs around four thousand pounds, pretty much ensuring that it is ground-mounted, and probably located near the traditional electric meter or utility interface that separates the electric power grid from the building power system. These electrical connections are illustrated, for example, in FIG. 8 where, for simplicity, only one string combiner and one inverter are shown. It will be appreciated that large systems will certainly have more than one string combiner and often more than one inverter.
The limitations and problems of conventional photovoltaic systems, particularly commercial installations, include: a lack of self-diagnostics to identify wiring or panel faults, difficulty in discerning performance, both on an individual panel level as well as a string or system level, and a lack of actionable diagnostic and performance information.
The lack of self-diagnostic features in photovoltaic power generation systems results in spotty system quality that is highly dependent on the skill and care of the installers. Unfortunately, this often results in a common complaint that “we need more highly trained installers in the photovoltaic industry.” What is actually needed is a higher level of system sophistication with built-in diagnostics so that the installers do not need to be as highly trained. Highly reliable photovoltaic panels and interconnections can and do fail, or partially fail, but the power generation capability of photovoltaic installations is also affected by issues such as panel shading and/or soiling. While many, if not most, commercial photovoltaic installations are instrumented with respect to total power output, most panel or string-level failures are difficult to discern and virtually impossible to diagnose and locate without sending a qualified technician to the site.
The power generation performance of a photovoltaic system, that might include thousands of photovoltaic panels, depends on the power generation performance and connection of each individual panel. And yet, with today's products and interconnection methods, this information remains unavailable. In fact, many failures that affect power generation performance, sometimes significantly, are completely undetectable. In a large photovoltaic system, it is possible for five to ten percent of the equipment on the roof to never even be attached and have the situation go undetected. Even when data collection suggests that the power generation performance is sub-par, there is no little or no actionable information to assist in the diagnosis and repair of the problem. To find the problem, the technician needs to literally go on the roof, take apart the system and make measurements with hand-held instrumentation. Care must be taken during this process, since lethal voltages and currents are generated when the sun is out and there are no switches in the system to turn this power off.
A solution to the problem involves electronically collecting data from each photovoltaic panel in the array. As part of the solution, an automatic a process has been developed by which photovoltaic panels are easily identified and addressed, and those addresses associated with physical locations. As an example of an analogous situation, consider a computerized office with a network. Now consider installing several-hundred or more networked printers on the computer network, where each printer is a plug-and-play printer so that receives an address. Although a user may be able to “see” and print to each of the printers, without more information (e.g., a description indicating the location of the printer), the user would have little likelihood of success picking a desired printer to use as the user would have to distinguish between self-assigned printer names having few distinguishing characters.
The same potential problem exists for large photovoltaic installations—there is no addressing protocol that, even if there is a determination of a wiring fault or poor performance, would enable easy location and repair or replacement of panels and wiring. Hence, one aspect of the present invention is directed to an efficient protocol to enable intelligent or smart panels to self-identify so as to associate the panel with a string, and determine the panel's position within the string, so as to enable reliable, repeatable (e.g., upon replacement of a panel in a string) addressing to quickly identify a panel's location within an array without having to enter, record and track pre-programmed panel identification data such as serial numbers and the like. Moreover, the addressing protocol disclosed in accordance with an aspect of the present invention further permits verification of the panel upon installation/replacement in order to facilitate installation, later shifting of panels, etc.
This lack of information also affects the installation process resulting in both higher installation costs and lower average system quality. Systems are wired and tested manually at each step of the way. Errors, which can be costly when they occur, are avoided only by trained technicians with hand-held instrumentation performing methodical test, measurement and installation processes effectively and fastidiously.
There are, in the marketplace, inverters called string inverters, which conventionally have a capacity of two to six peak kilowatts each. It is possible to build a commercial photovoltaic system using many of these relatively small inverters, and in that case there is information available as to the power output of each string of photovoltaic panels (usually between ten and twenty panels). Building photovoltaic power systems using string inverters provides some level of localization of wiring failures and performance problems.
However some shortcomings of using multiple string inverters in large commercial systems versus using one inverter include: the higher cost of multiple inverters; the higher weight added to a building roof; significant additional wiring cost; the lack of panel level performance information; and the problems in the installation process previously mentioned are not solved. Further, significant data processing problems in aggregating performance information for an entire photovoltaic power generation site are not addressed. Consequently standardized data collection, analysis and reporting for multiple sites is not yet possible.
Therefore, one aspect of the present invention is directed to a panel sentry for monitoring a photovoltaic panel, comprising: a source of power; a first circuit for detecting a power characteristic of the photovoltaic panel and producing a first signal representing the power characteristic of the photovoltaic panel; an electrical conductor serially connecting a power terminal of the photovoltaic panel to a power terminal of an adjacent panel; a second electrical conductor, also connected to the adjacent panel, said second conductor carrying a signal indicating a power characteristic of the adjacent panel; a second circuit for producing a second signal representing the power characteristic of the adjacent panel; and a transmitter for transmitting the first and second signals, said transmitter being powered by the source of power.
A further aspect of the present invention is directed to a method for monitoring the performance of a plurality of photovoltaic panels in an array, comprising: requesting datasets from a plurality of string sentries associated with the array, wherein the request includes status information for every string sentry and every panel sentry associated with the array; and collecting, using a bidirectional communication channel, and storing datasets from a master string sentry.
Yet another aspect of the present invention is directed to a method for addressing a plurality of monitoring devices, each monitoring device associated with a photovoltaic panel in an array of panels, comprising: initiating a request for information from a string of panels in the array; a string sentry selects a string address and initiates bi-directional communication with the string by sending a query; and the query is received and a response is generated for transmission by a panel sentry, wherein the panel sentry transmits its string and panel information to at least one adjacent panel in the string.
Yet a further aspect of the invention is directed to a method for the configuration and installation of a photovoltaic panel array, comprising: establishing as a minimal site computer configuration, a number of panels per string; placing at least one string sentry and a site computer in an installation mode; repeatedly polling the at least one string sentry to request data relating to the string sentry and any photovoltaic panels connected thereto; and receiving, at a panel sentry associated with a photovoltaic panel, a request and transmitting a response to the request, wherein the data transmitted includes a location identifier for the panel sentry, wherein upon receiving a subsequent request the panel sentry will also receive panel status data for driving a panel indicator associated therewith.
Another aspect of the present invention is directed to a panel sentry for monitoring a first photovoltaic panel, the panel sentry including a source of power, a first panel voltage detector detecting a first voltage produced by the first panel and producing a first signal representing the first voltage, a microcontroller in bi-directional communication with an external device and electrically connected to the first panel voltage detector and electrically connected to the source of power, the microcontroller receiving the first signal from the first voltage detector and transmitting the first signal to the external device and a memory storing a digital representation of the first signal.
Another aspect of the present invention is directed to a string sentry for monitoring at least one string of photovoltaic panels the string sentry including a source of power, a current detector detecting the total current produced by a string of panels and producing a signal representing the current, a microcontroller in bi-directional communication with at least one external device and electrically connected to the current detector and electrically connected to the source of power, the microcontroller receiving the signal from the current detector and transmitting the signal to the external device and a memory storing a digital representation of the signal representing the current.
A further aspect of the present invention is directed to a method for monitoring at least one string of photovoltaic panels including collecting, using a string sentry, a value of a current from a string of photovoltaic panels, storing, in the string sentry, the value of the current of a string of photovoltaic panels and transmitting the value of the current from the string sentry to an external computer.
Yet another aspect of the present invention is directed to a system for monitoring an array of photovoltaic panels the system including a plurality of panel sentries, each panel sentry electrically connected to a panel, a plurality of string sentries, each string sentry electrically connected to at least one string of panels, a site data concentrator in bi-directional communication with all string sentries in the system and a site computer in bi-directional communication with the site data concentrator and with an external computer.
A further aspect of the present invention is directed to a method for monitoring an array of photovoltaic panels the method including collecting, from all strings of panels in the array, a value of a current of the string, storing, in a site computer, the value of the current of the string of all strings of panels in the array, computing, using the site computer, an operational status of the array, making the stored value of the current of the string, of all strings of panels in the array, available for access and making the operational status available for access.
Yet another aspect of the present invention is directed to a system for monitoring one or more arrays of photovoltaic panels the system including a plurality of panel sentries, each panel sentry electrically connected to a panel, a plurality of string sentries, each string sentry electrically connected to a plurality of strings of photovoltaic panels, a plurality of site data concentrators, each site data concentrator in bi-directional communication with a site computer and in bi-directional communication with at least one string sentry in an array, a plurality of site computers each site computer in bi-directional communication with both a site data concentrator and a central computer, and the central computer in bidirectional communication with all site computers in the system, the central computer including a memory, the memory storing information transmitted from at least one of the site computers.
A further aspect of the present invention is directed to a method for monitoring one or more arrays of photovoltaic panels the method including monitoring all panels in all arrays using a panel sentry electrically connected to each panel, monitoring all groups of strings of panels in all arrays using a string sentry, each string sentry electrically connected to a group of strings, storing, in a central computer, a value of a current of a string, from all strings of panels in all arrays being monitored, storing, in the central computer, an operational status of all arrays being monitored, making the stored value of the current of the string, of all strings of panels in all arrays being monitored, available for access; and making the operational status, of all arrays being monitored, available for access.